Underground barrier for detecting hollows and a method of use thereof

ABSTRACT

An underground barrier for detecting underground hollows, comprising: a drilling rig; at least one drillstring, a proximal end of the drillstring, fitted on the drilling rig, the drillstring capable of drilling a borehole into the ground; a directional drilling unit, fitted on a distal end of the drillstring, capable of steering the drillstring in a desired path; a sensor unit, fitted on the distal end of the drillstring, capable of mapping the ground and hollows around the drillstring; and a control station; the control station configured to preform one or more of the following: control, the directional drilling unit to steer the drillstring in a desired path; receive, mapping data of the ground around the drillstring from the sensor unit; analyze, the mapping data received to detect underground hollows; and display, to a user of the system, using a user interface, the mapping data and the underground hollows.

FIELD OF THE INVENTION

The present invention relates to a system and method for an underground barrier that can detect irregularities and changes in underground soil and structure in order to alert of the presence of underground hollows and passages that may be used for the movement of people and goods across a boundary line.

BACKGROUND

The invention belongs to the area of “underground barrier” or “underground fence”. The term “underground barrier” refers to any measure that is used to detect the movement under ground level, of people or goods across a line separating area A from area B. This line may be—for example—a country border (where A is the country and B is a neighboring country), the circumference of a premises, or a battle line separating two enemy people.

A specific example of such a line is the border between the US and Mexico, where man-made underground passages were discovered in the past. Another specific example may be the border between North and South Korea.

“Underground barriers” refer to means to detect, and thus prevent, the passage of goods and humans. Goods are any of equipment, food and drugs etc.

Initiatives of constructing underground barriers go back many decades.

Current underground barriers of basic design are known to have one or more of the following components:

-   -   A wall. This can be a concrete wall going down below ground         level for tens of meters (vertically) and all along a border         line.     -   A trench. A deep trench used to be set as part of the wall of         fortified cities (e.g. Acre, Caesarea).     -   Sensors. These consist of ground sensors which aim to detect         changes in the underground environment, changes that are related         to attempt to create a hollow or a passage to cross the border         line.

The measures currently used in underground barriers may be classified as “detect active” or “detect passive”. By “detect active” we mean detecting the existence of work being done in order to build an underground hollow or passage; or detecting the actual attempt to cross the line by the underground hollow or passage, while it is occurring. “Detect passive” means detection of the existence of underground hollows or passages, a detection that may be while or after the hollows are made. “Detect passive” does not rely on present activity of the intruder.

The present invention provides the ability to detect passively and actively, being able to detect existing hollows and passages in the ground, and able to detect them as they are created.

Prior art underground barriers are costly to design and erect due to the difficulties to construct a substantial barrier underground. Even after such a barrier is constructed, there are difficulties in maintenance of the barrier and in monitoring that the barrier has not been breached.

Current sensors used with underground barriers, such as seismic and acoustic sensors, are limited by the structure and composition of the ground they are trying to sense through and usually can detect hollows only a few meters below ground level.

There is thus a need in the art for a new system and method for an underground barrier.

Korean Patent No. 101271689 (Sang-Wook et al.) discloses a method for locating tunnels. The method consists of having two vertical boreholes. A transmitter is inserted in one borehole, and a receiver is inserted into the other one, in a coordinated manner

The disclosed method of Sang-Wook et al. does not provide a manner of moving the transmitter and receiver through the boreholes, and does not provide a single transmitter-receiver solution and covers a very small area for each couple of horizontal boreholes so that many dozens of vertical boreholes will be required per every 1000 m of border length.

U.S. Pat. No. 8,396,610 (Mashiach) discloses a system that is based on autonomous vehicles traveling in pre-laid pipes.

The disclosed system of Mashiach does not disclose how the pipes, that are a prerequisite to moving vehicles in them, are laid underground. Further, it does not handle the communication difficulties of communicating with the autonomous vehicles underground and is limited in ease of deployment, and in maintenance of the deployed pipes and the complexity of the autonomous vehicles (e.g. how they are powered, and how they independently navigate).

U.S. Pat. No. 6,845,819 (Barret et al.) discloses a down hole tool “for logging and/or remedial operations in a wellbore in a hydrocarbon reservoir”.

The disclosed system of Barret et al. does not disclose and does not suggest using a system and method for an underground barrier.

SUMMARY

In accordance with a first aspect of the presently disclosed subject matter, there is provided an underground barrier for detecting underground hollows, comprising: a drilling rig; at least one drillstring, a proximal end of the drillstring, fitted on the drilling rig, the drillstring capable of drilling a borehole into the ground; a directional drilling unit, fitted on a distal end of the drillstring, capable of steering the drillstring in a desired path; a sensor unit, fitted on the distal end of the drillstring, capable of mapping the ground and hollows around the drillstring; and a control station; the control station configured to preform one or more of the following: control, the directional drilling unit to steer the drillstring in a desired path; receive, mapping data of the ground around the drillstring from the sensor unit; analyze, the mapping data received to detect underground hollows; and display, to a user of the system, using a user interface, the mapping data and the underground hollows.

In some cases, the control station is further configured to control the drillstring through a generally horizontal underground path.

In some cases, the control station is further configured to control at least two drill strings located in at least two adjacent generally horizontal underground paths.

In some cases, the control station is further configured to perform the following for controlling the drillstring through the desired path:

-   -   a) direct, the directional drilling unit to steer the         drillstring to drill from a current location through a generally         vertical path;     -   b) evaluate, the drillstring location to determine current depth         of the generally vertical path;     -   c) guide, the directional drilling unit to steer the drillstring         into a generally horizontal path, when a desired depth of the         generally vertical path is attained;     -   d) examine, the drillstring location to determine length of the         generally horizontal path;     -   e) return, the drillstring through the generally horizontal path         back to the generally vertical path, when a desired length of         the generally horizontal path is attained; and     -   f) repeat, steps a-e until parallel generally horizontal paths         have been drilled, a desired overall depth of the generally         vertical path is attained and underground area is mapped for         hollows.

In some cases, the control station is further configured to preform one or more of the following: monitor, the detection of one or more hollows in an underground area designated by the user of the system through the user interface; and alert, the user of the system through the user interface when one or more hollows are detected in the underground area.

In some cases, the sensor unit includes one or more of the following:

a. a borehole ground penetrating radar;

b. a seismic sensor;

c. a magnetometer;

d. an electrical resistivity sensor;

e. an acoustic sensor; or

f. an electromagnetic sensor using high-frequency radio waves.

In some cases, the directional drilling unit is a rotary steerable unit.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, with regard to the embodiments described, reference is made to the accompanying drawings, in which:

FIG. 1 is a schematic illustration of an environment of a system for an underground barrier, in accordance with the invention;

FIG. 2 is a schematic illustration of a side view of an embodiment of a system for an underground barrier, in accordance with the invention;

FIG. 3 is a schematic illustration of a view from above, of an embodiment of a system for an underground barrier, in accordance with the invention;

FIG. 4A is a schematic illustration of an embodiment of a system for an underground barrier, in accordance with the invention;

FIG. 4B is a schematic illustration of another possible embodiment of a system for an underground barrier, in accordance with the invention;

FIG. 5 is a schematic illustration of a detailed setting of a system for an underground barrier, in accordance with the invention;

FIG. 6 is a schematic illustration of a view from above, of a detailed setting of a system for an underground barrier, in accordance with the invention;

FIG. 7 is a schematic illustration of another possible embodiment of a system for an underground barrier, in accordance with the invention;

It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. Reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. There is no intention to limit the invention to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

In a general overview, some of the elements of the invention include technologies commonly used by the oil and gas industry, where they are typically used to search for underground resources, e.g. drilling for gas or oil.

Drilling is a process of making boreholes. A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water, other liquids (such as petroleum) or gases (such as natural gas), as part of a geotechnical investigation, environmental site assessment, mineral exploration, temperature measurement, as a pilot hole for installing piers or underground utilities, for geothermal installations, or for underground storage of unwanted substances, e.g. in carbon capture and storage.

There are two technology areas described herein:

A. Rotary steerable systems (RSS), which is a tool and form of drilling technology used in directional drilling. It employs the use of specialized downhole equipment that allows a user to optimize directional drilling. RSSs allow continuous rotation of the drillstring while steering the bit.

B. Sensors, used in measurement and logging while drilling the borehole through the desired path. In particular the current invention may make use of a ground penetrating radar (GPR), of which the borehole variant is called borehole radar (BHR).

Borehole radars utilizing GPR are used to map the structures from a borehole in underground applications. Modern directional borehole radar systems are able to produce three-dimensional images from measurements in a single borehole.

The BHR is a cylindrical assembly that is connected as part of the bottom hole assembly (BHA) of the drillstring. Since the drillstring rotates, the BHR is connected to the drill string with bearings to prevent it from rotating while operating (during capture of radar images). Alternatively the BHR may rotate at a controlled speed gathering a 360 degrees image of the borehole vicinity.

Several other sensor technologies may be used, such as acoustic sensors, magnetometers and seismic sensors. Another useful type of sensors are electrical resistivity sensors, which are used with advanced processing to form ‘electrical resistivity mapping’, also known as ‘electrical resistivity tomography’.

The present invention provides an improved barrier that consists of one or more horizontal underground boreholes in which sensors borne on a drillstring (such as a BHR) are deployed. The sensors provide a mapping of the ground around the borehole, as the drillstring drills through the desired path (radially, in all directions).

Analysis of the information, is performed in a control station, from several horizontal boreholes in which the sensors are deployed—a vertical plane of an underground barrier is constructed. The barrier enables to detect any attempt, going through hollows, to pass the vertical underground plane of the barrier and to alert such an attempt to a user.

The sensor data is analyzed in the control station to:

-   1. Detect hollows in underground by analysis of the collected data     from the sensors, in particular by studying discrepancies; and -   2. Compare to previous sensors runs—along the same underground area,     in order to detect changes (i.e. new hollows).

Some of the many advantages of the invention include the following non-limiting examples:

-   1. Fast deployment. The rate of borehole drilling can be dozens of     meters per day, and directional drilling methods are improving daily     (in particular by the oilfield services companies). -   2. The barrier may be implemented along a border line or along a     line that is out of the actual border line (e.g. run the barrier 100     m beyond the protected area). -   3. Unlimited depth. The barrier can go as deep as needed even over     than hundreds of meters. -   4. Very small—or none at all—footprint above ground. Footprint above     ground can be made away from the border line. -   5. Can be easily upgraded—as the GPR and other sensing technology     evolve (because the sensors are installed in a non-stationary     fashion). -   6. Difficult to detect. The boreholes are relatively small, deep in     the ground. -   7. Proven technology of the equipment used. Drilling, sensing, data     collection, data transmission, and data analyzing and imaging. -   8. Sustainability. A “break” of a branch can be easily repaired,     maintaining the barrier in full operating condition.

A preferred embodiment utilizes a drill string that may include a rotary steerable system and sensors part of the drillstring, such as PowerDrive ICE Ultra HT© by Schlumberger™, which includes TeleScope ICE©.

For BHR, a tool such as developed by T&A TISA® “3D Borehole Radar” may be added in the drillstring, or tools such as provided by Geomole™ (now CRCMining™). For Seismic imaging by borehole tools, there are tools from several companies, and an example is by Schlumberger™. Above ground monitoring and control station may include THEMA™ a drilling operation support and analysis tool, provided by Schlumberger™.

The drill string may contain the sensors assembly on the first drill (when the borehole is first drilled) or on following passes through the already drilled borehole. The sensors assembly, containing for example the GPR \ BHR, is run through the already drilled borehole periodically. Periodically means—for example—every several days or weeks. These runs are done to check changes in the underground, such as new hollows that were formed. For an efficient, time saving and lower cost drill, a coiled tubing drilling system may be used.

Coiled tubing drilling operations proceed quickly compared to using a jointed pipe drilling rig because connection time is eliminated during tripping. Coiled tubing drilling is economical in several applications, such as drilling slimmer wells, areas where a small rig footprint is essential, reentering wells and drilling underbalanced. For re-entry purposes, coiled tubing may be the preferred method.

Examples of coiled tubing drilling are available at:

http://www.slb.com/services/well_intervention/coiled_tubing/ctdirect-coiled-tubing-directional-drilling-system.aspx, And—https://www.youtube.com/watch?v=JomDgySCbM4&feature=youtube.

Alternatively or additionally, for re-entry to the borehole, a wireline method can be used. Wireline usually refers to a cabling technology used by operators of oil and gas wells to lower equipment or measurement devices into the well for the purposes of well intervention, reservoir evaluation, surrounding geology data collection, and pipe recovery.

Wireline may provide an advantage of speed and depth. In recent years, wireline methods also enable efficient re-entry of horizontal wells.

Bearing this in mind, attention is drawn to FIG. 1, showing a schematic illustration of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, at ground level surface 10, a drilling rig 12 and a control station 14 are stationed. A borehole 16 is drilled vertically into ground 20. At a desired depth the borehole turns to be horizontal 18.

The borehole 16 is drilled by a drillstring 22. The drillstring 22 is connected to the drilling rig 12. The drilling rig 12 can be located at ground level or located at an underground facility, thereby leaving no footprint above ground. The drillstring 22 can span from hundreds to thousands of meters long, from the drilling rig 12 all the way to the end of the borehole 16 underground. The lower part of the drillstring 22 is called the bottom hole assembly (BHA) 24.

In a preferred embodiment, the BHA 24 consists of a front portion “F”, which includes at least the bit 34 and a rear portion “R” 36 which connects the BHA 24 to the drillstring 22. The BHA 24 includes directional drilling equipment such as an RSS. The BHA 24 also includes measurement equipment (including various sensors) described as SENSE 32 in FIG. 1. SENSE 32 includes the equipment for collecting, logging, and transferring data to the control station 14 while drilling. SENSE 32 may further include equipment to receive communications from the control station 14 to control the operation of the sensors.

Attention is now drawn to FIG. 2, schematically illustrating a side (cut) view of an embodiment of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, a drilling rig 12 and a control station 14 are stationed at ground level 10. A vertical borehole path 16 is drilled by the drillstring 22, from which horizontal boreholes branch 40, 42, 44, 46. At a depth of D1 41 a horizontal borehole 40 is drilled. At a depth of D2 43 another horizontal borehole 42 is drilled. Additional horizontal boreholes 44 and 46 may be drilled to make the barrier cover deeper areas into the ground, where the overall depth is determined according to the depth required for the underground barrier. As shown in branching borehole 46, the borehole may run in a path which is not only horizontal: going upward or downward as needed, controlled by the user of the control station. The user may also steer the drillstring 22 in any navigation azimuth to create a preferred path.

In a preferred embodiment, the vertical gaps between the horizontal boreholes, such as D2-D1 in FIG. 2, are selected according to at least the following: (a) soil properties and structure (b) SENSE 32 technology and capabilities (c) the required resolution, i.e. the size of hollow that is needed to be detected (higher resolution will require smaller gaps).

Attention is now drawn to FIG. 3, a schematic illustration of a top (aerial) view of an embodiment of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, the drilling rig 12 is shown, from which the horizontal underground boreholes paths branch. Path 40, 48 and 52 are examples. Path 50 is another example of a borehole path that goes first vertically (the same as borehole 16 in FIG. 2) and then horizontally 50 across a borderline 64 that is to be protected, and then continues horizontally 52 along the borderline or in any other azimuth, according to the user input via the control station 14.

Attention is now drawn to FIG. 4A, a schematic illustration of an embodiment of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, the BHA 24 is deployed through borehole path 40, at time T1. While moving through the borehole path 40 the SENSE 32 attached to the BHA 24, which in one preferred embodiment includes a BHR, sends electromagnetic radar waves around the borehole in all directions, and obviously above 54 and below 55 the horizontal borehole path 40. The BHR survey results in an image representing the status of the ground around the BHA 24. After going through horizontal borehole path 40, the drillstring 22 is pulled back to the vertical borehole path 16 and then oriented at time T2 into an additional horizontal borehole path 42. Moving through horizontal borehole path 42, the BHA 24, utilizing the SENSE 32 attached to it, maps the ground above 56 and below 57 the additional horizontal borehole path 42. This enables a full coverage of the ground section from ground level 10 to any required depth (by adding more horizontal boreholes). The mapping analysis process can be done via the control station 14 while the boreholes are drilled, or at any time after they were drilled.

Attention is now drawn to FIG. 4B, a schematic illustration of another embodiment of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, FIG. 4B is a broader embodiment of FIG. 4A. As shown in FIG. 4B, moving through horizontal borehole path 40 and 40A, the BHA 24 and 24A, utilizing the SENSE 32 attached to it, maps the ground above 54, 54A and below 55, 55A respectively. Moving through the boreholes 40 and 40A may be done in a coordinated manner or none coordinated manner Also, BHA 24, 24A may include sensors that are transmitter and receiver in the same unit or one (e.g. 24) including a transmitter and the other (e.g. 24A) including a receiver of the signals. Sensors included in BHAs 24 and 24A may be of various types as mentioned above.

In another embodiment the underground barrier, the underground barrier is built by boreholes made from more than one vertical borehole paths 16 and 16A. Illustrated are two examples of horizontal borehole paths 40 and 40A branching from vertical borehole paths 16 and 16A respectively. The BHAs 24 and 24A correspond to the two drillstrings 22 and 22A.

In this embodiment, BHAs 24 and 24A, utilizing the SENSE 32 attached to them, map the ground around the horizontal borehole paths 40 and 40A, while moving in a coordinated manner through horizontal borehole paths 40 and 40A.

In this embodiment, BHAs 24 and 24A may also be a receiver and transmitter, such as, for example, BHA 24 is a transmitter only, transmitting signals to be received by BHA 24A SENSE 32 sensors in order to analyze the underground between borehole paths 40 and 40A.

In a further embodiment the BHA 24 and 24A move through borehole paths 40 and 40A with no coordination at the same time or at different time.

Attention is now drawn to FIG. 5, a schematic illustration of a detailed setting of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, zone A 60 is the area to be protected by the underground barrier of the disclosed subject matter, with a protected building 66 inside, along the border of zone A 64 or beyond it, into zone B 62. The barrier along the border of zone A 64 may optionally include an above ground barrier, e.g. a fence 68, and an underground barrier consisting of multiple underground boreholes paths 72, 74, 76, and 78.

The drawing of FIG. 5, illustrates that while the above ground barrier 68 is placed on the border line 64 between zone A 60 and zone B 62, the underground barrier may actually be placed inside and underground zone B 62, at a distance L1 80 beyond the border line 64. This may be done by implementing a horizontal borehole path 70 that crosses the border underground, from which other horizontal borehole paths 76 and 78 will branch.

Attention is now drawn to FIG. 6, a schematic illustration of a top (aerial) view of a detailed setting of a system for an underground barrier, in accordance with the presently disclosed subject matter.

According to certain examples of the presently disclosed subject matter, horizontal borehole paths 76 and 77 may cover segments of the border line 64. An Additional drilling rig 13 can be placed along the border line 64 to cover additional segments of the border line 64 with more horizontal borehole paths 84 and 85. The L1 80 and L2 83 denote possible locations of placing an underground barrier like the horizontal borehole paths 76 and 77. L2 83 depicts a position 82 of a possible barrier within the zone A 60, with a protected building 66 inside that zone A 60. One or more underground barriers may be set, on the border line 64 outside 76 or inside 82 zone A 60. This acts both as redundancy and plots the direction of underground hollows or other discrepancies.

Attention is now drawn to FIG. 7, a schematic illustration of another possible embodiment of a system for an underground barrier, in accordance with the presently disclosed subject matter.

Another embodiment is disclosed, of a system for an underground barrier comprising of a vertical borehole path 16 that branches into a horizontal borehole path 100 and from the horizontal borehole path 100, branches in multiple directions vertical borehole paths 102, 104, 106 and 108 which may be at an angle with the horizon. The angle, such as 120 and 121 may vary. A vertical borehole path 108, may turn into a horizontal borehole path 110. Also, a path may be routed according to any needs (e.g. ground structure, underwater, soil characteristics), to go into a horizontal borehole path 112, tending “upward” 113, “downward” 114 and horizontally again 116. It may also be routed across the border line 64, parallel to the border line out of the premises 60, under the border line 134 or inside the premises area 136 parallel to border line 64 or at any other direction. It may also be routed 130 across the border line 64, parallel to the border line 132 out of the premises 60, under the border line 134 or inside the premises area 136 parallel to border line 64 or at any other direction.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. 

1. An underground barrier for detecting underground hollows, comprising: a drilling rig; at least one drillstring, a proximal end of the drillstring, fitted on the drilling rig, the drillstring capable of drilling a borehole into the ground; a directional drilling unit, fitted on a distal end of the drillstring, capable of steering the drillstring in a desired path; a sensor unit, fitted on the distal end of the drillstring, capable of mapping the ground and hollows around the drillstring; and a control station; the control station configured to preform one or more of the following: control, the directional drilling unit to steer the drillstring in a desired path; receive, mapping data of the ground around the drillstring from the sensor unit; analyze, the mapping data received to detect underground hollows; and display, to a user of the system, using a user interface, the mapping data and the underground hollows.
 2. The underground barrier of claim 1, wherein the control station is further configured to control the drillstring through a generally horizontal underground path.
 3. The underground barrier of claim 1, wherein the control station is further configured to control at least two drill strings located in at least two adjacent generally horizontal underground paths.
 4. The underground barrier of claim 1, wherein the control station is further configured to perform the following for controlling the drillstring through the desired path: a) direct, the directional drilling unit to steer the drillstring to drill from a current location through a generally vertical path; b) evaluate, the drillstring location to determine current depth of the generally vertical path; c) guide, the directional drilling unit to steer the drillstring into a generally horizontal path, when a desired depth of the generally vertical path is attained; d) examine, the drillstring location to determine length of the generally horizontal path; e) return, the drillstring through the generally horizontal path back to the generally vertical path, when a desired length of the generally horizontal path is attained; and f) repeat, steps a-e until parallel generally horizontal paths have been drilled, a desired overall depth of the generally vertical path is attained and underground area is mapped for hollows.
 5. The underground barrier of claim 1, wherein the control station is further configured to perform the following for controlling the drillstring through the desired path: a) direct, the directional drilling unit to steer the drillstring to drill from current location through a generally horizontal path; b) evaluate, the drillstring location to determine current length of the generally horizontal path; c) guide, the directional drilling unit to steer the drillstring into a generally vertical path, when a desired length of the generally horizontal path is attained; d) examine, the drillstring location to determine depth of the generally vertical path; e) return, the drillstring through the generally vertical path back to the generally horizontal path, when a desired depth of the generally vertical path is attained; and f) repeat, steps a-e until parallel generally vertical paths have been drilled, a desired overall depth of the generally horizontal path is attained and underground area is mapped for hollows.
 6. The underground barrier of claim 1, wherein the control station is further configured to preform one or more of the following: monitor, the detection of one or more hollows in an underground area designated by the user of the system through the user interface; and alert, the user of the system through the user interface when one or more hollows are detected in the underground area.
 7. The underground barrier of claim 1, wherein the sensor unit includes one or more of the following: a. a borehole ground penetrating radar; b. a seismic sensor; c. a magnetometer; d. an electrical resistivity sensor; e. an acoustic sensor; or f. an electromagnetic sensor using high-frequency radio waves.
 8. The underground barrier of claim 1, wherein the directional drilling unit is a rotary steerable unit.
 9. The underground barrier of claim 1, wherein said drilling rig is a coiled tubing drilling rig.
 10. A method comprising: providing control, by a control station, of a directional drilling unit, fitted on a distal end of a drillstring, capable of drilling a borehole into the ground, at least one proximal end of the drillstring fitted on a drilling rig, to steer the drillstring in a desired path; receiving, mapping data of the ground and hollows around the drillstring from a sensor unit, fitted on the distal end of the drillstring, capable of mapping the ground and hollows around the drillstring; analyzing, the mapping data received to detect one or more underground hollows; and displaying, to a user of the system through a user interface the mapping data and the underground hollows.
 11. The method of claim 10, wherein the control station is further configured to control the drillstring through a generally horizontal underground path.
 12. The method of claim 10, wherein the control station is further configured to control at least two drill strings located in at least two adjacent generally horizontal underground paths.
 13. The method of claim 10, further comprising: a) directing, the directional drilling unit to steer the drillstring to drill from current location through a generally vertical path; b) evaluating, the drillstring location to determine current depth of the generally vertical path; c) guiding, the directional drilling unit to steer the drillstring into a generally horizontal path, when a desired depth of the generally vertical path is attained; d) examining, the drillstring location to determine length of the generally horizontal path; e) returning, the drillstring through the generally horizontal path back to the vertical path, when a desired length of the horizontal path is attained; and f) repeating, steps a-e until parallel generally horizontal paths have been drilled, a desired overall depth of the generally vertical path is attained and underground area is mapped for hollows.
 14. The method of claim 10, further comprising: a) directing, the directional drilling unit to steer the drillstring to drill from current location through a generally horizontal path; b) evaluating, the drillstring location to determine current length of the generally horizontal path; c) guiding, the directional drilling unit to steer the drillstring into a generally vertical path, when a desired length of the generally vertical path is attained; d) examining, the drillstring location to determine depth of the generally vertical path; e) returning, the drillstring through the generally vertical path back to the generally horizontal path, when a desired depth of the generally vertical path is attained; and f) repeating, steps a-e until parallel generally vertical paths have been drilled, a desired overall depth of the generally horizontal path is attained and underground area is mapped for hollows.
 15. The method of claim 10, further comprising: monitoring, the detection of one or more hollows in an underground area designated by the user of the system through the user interface; and alerting, the user of the system through the user interface when one or more hollows are detected in the underground area.
 16. The method of claim 10, wherein the sensor unit includes one or more of the following: a. a borehole ground penetrating radar; b. a seismic sensor; c. a magnetometer; d. an electrical resistivity sensor; e. an acoustic sensor; or f. an electromagnetic sensor using high-frequency radio waves.
 17. The method of claim 10, wherein the directional drilling unit is a rotary steerable unit.
 18. The method of claim 10, wherein said drilling is performed using the coiled tubing drilling method. 